Quickly and accurately estimating locations of people in a geographic area can be used to speed up emergency response times, track business assets, and link consumers to nearby businesses. Various positioning systems are used to estimate the position of a person, including satellite positioning systems, terrestrial positioning systems and hybrid versions of satellite and terrestrial positioning systems. Each system usually includes a receiver that: receives signals from satellite and/or terrestrial beacons; computes distances traveled by those signals; and then uses geometry to estimate its position using the computed distances and knowledge of each beacon's location.
The accuracy of the receiver's estimated position can be improved with knowledge that the receiver is inside a building (“indoors”) or outside a building (“outdoors”). Depending on where the receiver resides, positioning algorithms can be applied differently by exploiting previously known multipath profile information, accounting for signal strength loss due to building walls, weighing different signal constellations differently, and accounting for other considerations. Knowledge of whether a receiver is indoors or outdoors can also improve user experience by aiding the identification of appropriate building maps, and can be used to aggregate statistics such as what percentage of E-911 calls are made from indoor locations as from outdoor locations.
Unfortunately, techniques that estimate whether a receiver is indoors or outdoors lack precision and/or are too slow. Thus, there is a need for improved techniques to estimate whether the receiver is indoors or outdoors.